Mason Astrophysicists Develop Technique for “Weighing” Black Holes

Black holes are often misunderstood by the general public. While frequently used as a figure of speech for where that missing sock went or as a radical time travel vehicle for science fiction movies, a black hole is in actuality the death of a star — and one of the great mysteries scientists are still pondering about space.

Lev Titarchuk

George Mason scientist Lev Titarchuk, professor of computational and data sciences, and his former PhD student and Mason alumni Nikolai Shaposhnikov are working to solve the mystery of black holes. The two have successfully tested a new method for determining the masses of black holes — one of the first steps in identifying and exploring these extremely dense objects in space.

The technique, which Titarchuk has been working on for nearly a decade, looks at the relationship between a black hole and the surrounding disk of matter spiraling into it, called an accretion disk. Gas orbiting in these disks eventually falls into the black hole.

As particles in the accretion disk get closer to the black hole, they build up and crash into each other in a way that Titarchuk likens to a car accident or traffic jam. He determined that the distance from the black hole to the accretion disk is on a direct scale with the mass of the black hole — and using these proportions and the oscillation frequency of particles in the accretion disk, is able to “weigh” a black hole with a very small margin of error.

A blue supergiant star (right) and a black hole are depicted above. The black hole is surrounded by a gaseous accretion disk that is fed by the star. Some black holes emit jets along the polar axis, as shown here.NASA/Honeywell Max-Q Digital Group/Dana Berry image

Titarchuk and Shaposhnikov have proven their method using six different black holes. For example, they have shown that the black hole in a binary system known as Cygnus X-1 —t he first compelling black hole candidate to emerge in the early 1970s — contains 8.7 times the mass of our sun, with a margin of error of just 0.8 solar mass.

A paper outlining their results is scheduled to appear in the July 1 issue of Astrophysical Journal.

“Our method can measure a black hole’s mass when the method of using optical observations fail,” says Titarchuk, who also works at NASA’s Goddard Space Flight Center in Greenbelt, Md., and at the Naval Research Laboratory in Washington, D.C.

Shaposhnikov, who graduated from Mason in 2004 with his PhD in Computational Sciences and Informatics, works for the Universities Space Research Association, a part of the Center for Research and Exploration in Space Science and Technology within NASA Goddard.

This method will have important implications in understanding how black holes originate and change, and is already being used for new discoveries. Using Titarchuk’s method in their own work, Tod Strohmayer and Richard Mushotzky from NASA Goddard have examined masses thought to be intermediate black holes. An intermediate-mass black hole is a black hole whose mass is significantly more than stellar black holes, which have a mass only a few times greater than the mass of the sun, yet far less than the mass of supermassive black holes that is a few million times greater than the mass of the sun.

According to the NASA web site, the existence of intermediate black holes remains controversial because there is no widely accepted theory for how they could form. Therefore it is particularly important to have strong observational arguments and evidence for their existence in the universe.